What you should do is take the SCJA exam. It is on Java 1.5, but doesn't go too in depth on Java 1.5 constructs. You don't need to know RegEx or anything like that, just basic syntax for Generics and a for:each loop.

So, get you SCJA certification on Java 1.5, and you can say that you are Java 5 certified on your resume.

Then, take SCJP 1.4, which is said to be a bit easier than the SCJP 1.5 exam. So, then you can advertise both being a Sun Certified Java Programmer, and a Sun Certified Java Associate, on Java versions 1.4 and Java 5.

I would focus on the SCJP 1.5 exam, unless you have compelling reasons to take 1.4 instead (for example, if an employer insists on it). Yes, 1.4 is somewhat easier, but 1.5 is current, and the differences are significant.

Note that there are no prerequisites for the SCJP exam (SCJA is not required).